Fs81 with bad compression , Fix?

[Sean McGillicuddy]

Hello
I have a Stihl FS81 with bad compression.
Is this worth fixing?
How hard is it to fix?
How would I go about fixing it?
Thanks
Sean

 

[Jon1270]

Unless you really love it or have time to tinker, my guess is it's not worth fixing. I don't have much weedeater / brush cutter experience but it can't be much different from a chainsaw engine. These motors seem to fail because of air leaks, misadjusted carbs or straight-gassing more often than from simple wear. It's best to try and figure out what caused the failure before you tear it completely apart.

The piston and rings will almost certainly be toast, but cylinders are often salvageable. Dealer parts will be very expensive. Looking at eBay, there doesn't seem to be much of an aftermarket for this model. A couple of sellers are offering new OEM pistons, but for the price of a new piston and rings ($50) plus any gaskets and seals, wrist pin clips, etc. you could buy a complete used engine ($55-$65) which is what I'd probably do. Installation would me a matter of removing and replacing everything around it, i.e. all the plastic cowling, air filter, carb and intake assembly, muffler, flywheel, ignition coil, clutch, etc. Removing the flywheel from the old motor is probably the trickiest single operation, and even that's not hard. It would be important to set the gap between coil and flywheel carefully during reassembly. You might need to replace an intake gasket or two along the way, and adjust the throttle linkage, and when it's all back together you'd need to adjust the carb settings.

Unless you want a project, the smart move for you is probably to buy a replacement trimmer and trade in the old one for parts.

 

[Sean McGillicuddy]

 

[Jon1270]

Aww, there there. You can fix it if you want to.

 

[Danno77]

Is that a straight shaft trimmer?

 

[Sean McGillicuddy]

Straight shaft yes.
Do the sell a head unit?

 

[SCOTT S.]

15 yrs. on a weedwacker, I would say that's a good run, if it was me I would be shopping for a new toy.

 

[TreePointer]

If you plan on fixing similar engines in the future, this might be a good time to invest in a vacuum tester, compression tester, and some hand tools like the appropriate t-handle drivers. Not everyone has time or desire to do this, so buying a new one is the best option for some.

 

[Danno77]

Straight shaft yes.
Do the sell a head unit?

I dunno, I just wondered if you could buy the cheaper model and swap the head. I'm no trimmer expert, but might be an option.